The production of molded articles having a closed outer skin and cellular core by the isocyanate polyaddition process is known in principle (see, e.g., Kunststoffe 60, pages 3-7 (1970) or German Auslegeschrift No. 1,196,864). With suitable choices of the starting components, it is possible by this process to produce both elastic and rigid molded articles. If little or no blowing agent is used in this process, solid articles are obtained. Processing of the raw materials is preferably carried out by the reaction injection molding process (RSG or RIM process). This is a filling technique in which the liquid starting components are introduced into the mold within the minimum of time through so-called forceably-controlled mixing heads. In the production of molded parts for the automobile industry, for example, di- and/or tri-functional polyether polyols, for example, in the molecular weight range of from 3,000 to 7,000, and low molecular weight diols, such as ethylene glycol and/or butane-1,4-diol or aromatic diamines having sterically hindered amino groups, are thus reacted with polyisocyanates, preferably liquid polyisocyanates or polyisocyanate mixtures of the diphenyl methane series, optionally in the presence of blowing agents (see, e.g., U.S. Pat. Nos. 4,218,543 or 4,065,410).
The molded articles produced in this manner have excellent mechanical properties. It has been found, however, that the articles occasionally have a surface which is not completely free from depressions and pores. Such surface faults can be rendered visible by rubbing a colored powder into the molded article, with the faults creating a light scattering effect and lightening of the surface fault when compared with a deep black (colored with graphite), flawless surface. Moreover, these surface defects are often starting points for mechanical failures and damage.
Such surface defects in the form of pores or pin holes must often be filled in with a repairing or filling material applied by spatula. The repaired area must subsequently be rubbed down and possibly degreased either before or after this operation and optionally lacquered, making the removal of these surface defects involved and expensive.
It was therefore an object of the present invention to provide a process which would enable molded polyurethane articles to be produced without such surface defects. This problem was solved by the process according to the invention.